Vapor guard viscometer

ABSTRACT

Viscometer means are provided for monitoring, over extended periods, the viscosity of pharmaceutical capsule dipping solutions and the like, particularly solutions being mixed under exposure to air. The apparatus includes a rotational viscometer and viscometer spindle having guard means affording non-turbulent exposure to the moving liquid and protection for critical shear surfaces.

United States Patent Kenyon 1 Apr. 17, 1973 [54] VAPOR GUARD VISCOMETER 1,836,995 12/1931 I Stickney ..73 59 [75] Inventor: Nam R Kenyon Birmingham 2,142,854 1/1939 La Pierre ..73 59 m Primary ExaminerRichard C. Queisser Assigneel PqrkwDavis & p y, Detroit. Assistant Examiner loseph w. Roskos MlCh. Att0rney-R0bert R. Adams et al.

[22] Filed: Aug. 5, 1971 [57] ABSTRACT [21] App]. No.: 169,309

. viscometer means are provided for monitoring, over extended periods, the viscosity of pharmaceutical cap- U-S- t n i Cl- ..G0ln tions mixed under exposure to air T p [58] Field of Search ....73/59 paratus includes a rotational viscometer and viscome ter spindle having guard means affording non-turbu- [56] References Cited lent exposure to the moving liquid and protection for UNITED STATES PATENTS critical shear surfaces. 2,957,339 6 Clailm, 3 Drawin Figures 3 10/1960 Penny et a] ..73/59 PATENTEH AFRI 71973 INVENTOR- NAZAR P. KENYON BY M13, M ATTY.

VAPOR GUARD VISCOMETER SUMMARY AND DETAILED DESCRIPTION This invention relates to novel apparatus and means for measuring viscosity of pharmaceutical capsule dipping solutions and the like. More particularly, the invention concerns improved rotational viscometer means of the suspended spindle type.

Heretofore the art has commonly employed viscometer means having a rotational viscometer spindle which for some applications may be operated within a protecting tubular spindle guard. The prior art apparatus, however, has been limited in its application and is inadequate, for example, where there is varying exposure from run to run to secondary or extraneous shear surfaces or where the apparent viscosity over a period of time progressively increases due to local congealing or thickening, etc.

It is therefore an object of the present invention to provide improved apparatus and means for measuring the viscosity of pharmaceutical capsule dipping solution and the like and also for measuring the same on a continuous basis.

It is another object to provide means for measuring the viscosity of liquids which have an inherent tendency to congeal and thicken over a period of time.

It is also an object of the invention to provide means in measuring the viscosity of liquids for maintaining uniform exposure to critical shear surfaces from run to run. 7

These and other objects, purposes and advantages of the invention will be seen from the following description with reference to the accompanying drawing in which FIG. I is a view in elevation of a preferred viscometer and spindle tube according to the invention;

FIG. 2 is a side view in assembly showing means securing the tube to the viscometer mounting; and

FIG. 3 is a top view taken on line 3-3 of FIG. 1.

Referring to the drawing, FIG. 1 illustrates a preferred embodiment in which a viscometer is arranged for measuring the viscosity of a liquid 22 being cycled or mixed in a container such as the reservoir of a capsule dipping tank. The viscometer is mounted from a stationary bracket assembly 11 holding a leveling mount 12 which is mechanically adjustable to a level position by means of the adjustment screw 13, universal disc 13a, and socket 13b. A spindle 15 is suspended from the viscometer 10 by plumb line or spindle extension line 16. Extending downward at right angles from the leveling mount 12 is a mounting bracket 17 on which a spindle guard tube 18 is detachably mounted. The guard tube is generally cylindrical, open at both ends and conveniently made of adurable inert metal, preferably stainless steel polished for ease in cleaning. The lower end of the tube in the area adjoining the spindle 15 is provided with vent holes 18a, preferably evenly located in both axial and radial position with respect to the spindle position, the object being to balance the geometry of the shear surfaces particularly as between the spindle and the guard tube.

For mounting, hub 19a of the tube is inserted into recess 170 which serves to locate the tube within an axial channel 17b, thus assuring correct vertical alignment. The hub in turn is locked in position by the mounting screw 19. By these means the tube from time to time can be detached as required for cleaning purposes, etc., and remounted each time precisely in the same position relative to the spindle 15 and spindle line 16.

According to a preferred embodiment of the invention, the upper end of the tube which is open to the atmosphere is provided with a cover 20 hingeably mounted to the bracket 17 by mounting piece 200 and spacer 20b. The cover 20 serves to close the open end of the tube (FIG. 3) surrounding and spaced from the plumb line at the liquid interface and for a sufficient distance above the liquid, and thereby provides a confined zone inside the tube such that vapor given off from the liquid surface within the zone is substantially completely retained within the zone and is in equilibrium with the liquid surface; it also can be tilted upward by hinge means to the open position illustrated in dotted outline, FIG. 1. To secure the cover 20 in open position for cleaning purposes, etc., a cover lock 21a is provided. The cover 20 has a slotted opening 21b slightly narrower than the width of the cover lock 21a so that as the cover is swung open to the full position it compresses the cover lock and snaps onto it. The lock advantageously holds the cover away from the rotation axis, as appears below, for changeover purposes etc.

OPERATION In operation the viscometer 10 mounted above the body of liquid 22 on bracket 11 is adjusted to a level position, as illustrated, by adjustment of screw 13, leveling socket 13a and disc 13b. Next, the spindle guard 18 is mounted in position (with the lower end immersed in the liquid) and secured on a vertical line within channel 17b by tightening the mounting screw 19. The cover 20 is snapped into the fully open position dipping solution. Attempts in this regard using rotational viscometric means (for measuring the shear forces or tangential drag on the spindle) have in the past been unsatisfactory particularly for continuous measurement and over long periods of time. The problem is complicated by the fact that the viscosity of the dipping solution (usually aqueous gelatin) tends to vary at different locations in the clipping tank for various reasons such as incomplete mixing, local differences in temperature (the operating temperature being, for example, from l05-l25 F. and preferably from I l0l 15 F.), evaporation loss, etc. Surface drag is another problem due to progressive thickening of the dipping solution whereby viscosity measurement satisfactory at the start of the run becomes faulty or inaccurate in periods as short as 15 minutes. Also, while it is considered important for measurement purposes to maintain flow of the dipping solution to the spindle, there is a tendency for such flow to deflect the spindle and cause it to swing (that is, to undergo a pendulum for pharmaceutical capsule production over extended periods of time, up to 18 hours or more, has been completely satisfactory; The apparatus advantageously serves to eliminate undesirable adverse influences which interfere with accurate measurement of the viscosity, that is with measurement of the change in the shear rate due to the viscous change in the liquid itself. In particular, the spindle guard tube 18 protects the spindle and plumb line against interfering shear surfaces and assists in maintaining the dipping solution homogeneous throughout the confined zone with respect to viscosity and temperature, especially on the liquid surface 23 at point-24 where the plumb line is exposed to both air and liquid. The vent holes 18a serve to promote lateral (as opposed to vertical) circulation of the dipping solution at the surface of the spindle, i.e., the flow is adequate to insure constant change at the spindle surface such that the sample being measured is truly representative of theaverage liquid viscosity in the clipping tank. While the vent holes do provide for the desired flow, yet the venting effect is not excessive to the point that the spindle swings or undergoes a pendulum action. For purposes of illustration, a preferred venting configuration for a guard tube (1% inch D. 16 gauge 316 stainless tubing) is rows of holes inch in diameter) per row with A inch axial space between rows and 45 radial space between holes.

The apparatus of the invention is particularly welladapted for viscosity measurement of aqueous gelatin solutions but it will be realized that the invention can be used for solutions other than gelatin solutions, and in fact for liquid viscometry in general.

For preferred purposes in capsule production the'apparatus is used with forced flow dipping tanks of conventional design. For this application, the guard tube 18 is preferably located for free access, ordinarily in one of the open corners of the tank isolated from competing shear surfaces. Also, the tube should be located in precisely the same position from run to run, as indicated, to assure that the measurement each time will be reproducible.

While the invention in viscometer means has been described in considerable detail in the foregoing specification, it will be realized by those skilled in the art that wide variation can be made in such detail within the spirit of the invention claimed below. It is intended that the claims which follow be interpreted to cover both the invention particularly described and any such variation. 7

I claim:

1. ln viscometer apparatus comprising a spindle adapted to be held suspended on a torsion-transmitting plumb line for immersion in a flowing body of con- .gealable aqueous liquid and for rotation therein at a rate proportional to the viscosity of the liquid, the spindle being shielded in its rotation by a surrounding spindle guard tube having open upper and lower ends,

the improvement comprising a bracket having means for removably mounting the spindle guard tube,

a cover for the upper end of the guard tube adapted to provide a confined zone inside the tube such that vapor given off from the liquid surface within the zone is substantially completely retained within the zone and is in equilibrium with the liquid phase.

2. Apparatus according to claim 1 wherein the spindle guardis a tube apertured forliquid flow relative to the spindle at a rate such that the spindle is maintained substantially free of lateral motion relative to the spindle guard.

3. Apparatus according to claim 1 wherein the cover for the spindle guard tube is hingeably mounted on the bracket.

4. Apparatus according to claim 2 wherein the liquid is aqueous gelatin solution.

5. Apparatus according to claim 3 wherein the liquid is aqueous gelatin solution.

6. Apparatus according to claim 2 including means for detachably mounting the spindle guard in a capsule dipping tank. 

1. In viscometer apparatus comprising a spindle adapted to be held suspended on a torsion-transmitting plumb line for immersion in a flowing body of congealable aqueous liquid and for rotation therein at a rate proportional to the viscosity of the liquid, the spindle being shielded in its rotation by a surrounding spindle guard tube having open upper and lower ends, the improvement comprising a bracket having means for removably mounting the spindle guard tube, a cover for the upper end of the guard tube adapted to provide a confined zone inside the tube such that vapor given off from the liquid surface within the zone is substantially completely retained within the zone and is in equilibrium with the liquid phase.
 2. Apparatus according to claim 1 wherein the spindle guard is a tube apertured for liquid flow relative to the spindle at a rate such that the spindle is maintained substantially free of lateral motion relative to the spindle guard.
 3. Apparatus according to claim 1 wherein the cover for the spindle guard tube is hingeably mounted on the bracket.
 4. Apparatus according to claim 2 wherein the liquid is aqueous gelatin solution.
 5. Apparatus according to claim 3 wherein the liquid is aqueous gelatin solution.
 6. Apparatus according to claim 2 including means for detachably mounting the spindle guard in a capsule dipping tank. 